Pre-implantation Genetic Diagnosis Reduces Live Birth Rate
Oops. Here we have been told that PGD, that is, removing one cell from an early embryo and testing to determine whether it is deemed worthy of implantation, does not harm embryos. Not so, perhaps. According to a study published in the New England Journal of Medicine:
Preimplantation genetic screening did not increase but instead significantly reduced the rates of ongoing pregnancies and live births after IVF in women of advanced maternal age. These results argue strongly against routinely performing preimplantation genetic screening as an adjunct to IVF in this group of women.The study speculates on several potential causes:
Several mechanisms may be responsible for the failure of preimplantation genetic screening to improve the outcomes of IVF in women of advanced maternal age. It is possible that biopsy of a blastomere [cell] on day 3 of embryonic development hampers the potential of an embryo to successfully implant; however, the effect of biopsy alone on pregnancy rates has not been studied. Furthermore, the limitation in the number of chromosomes that can be analyzed with FISH could lead to the transfer of embryos labeled as normal that are in fact aneuploid for one or more chromosomes not tested. This problem may be overcome in the future by the use of new techniques, such as array comparative genomic hybridization, in which the complete ploidy status can be given for a blastomere after biopsy. Finally, many human embryos resulting from IVF may be mosaic, so that the chromosomal constitution revealed by analysis of the blastomere may not be representative of the entire embryo.Interesting stuff. It appears that our attempts at hyper-control of progeny has a ways to go.
No word yet on whether this outcome impacts Advanced Cell Technology's assertion that it can obtain ES cells without harming embryos which uses the same PGD technique.